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    Subject[085/111] sched: Fix granularity of task_u/stime()
    2.6.32-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>

    commit 761b1d26df542fd5eb348837351e4d2f3bc7bffe upstream.

    Originally task_s/utime() were designed to return clock_t but
    later changed to return cputime_t by following commit:

    commit efe567fc8281661524ffa75477a7c4ca9b466c63
    Author: Christian Borntraeger <borntraeger@de.ibm.com>
    Date: Thu Aug 23 15:18:02 2007 +0200

    It only changed the type of return value, but not the
    implementation. As the result the granularity of task_s/utime()
    is still that of clock_t, not that of cputime_t.

    So using task_s/utime() in __exit_signal() makes values
    accumulated to the signal struct to be rounded and coarse
    grained.

    This patch removes casts to clock_t in task_u/stime(), to keep
    granularity of cputime_t over the calculation.

    v2:
    Use div_u64() to avoid error "undefined reference to `__udivdi3`"
    on some 32bit systems.

    Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
    Acked-by: Peter Zijlstra <peterz@infradead.org>
    Cc: xiyou.wangcong@gmail.com
    Cc: Spencer Candland <spencer@bluehost.com>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Stanislaw Gruszka <sgruszka@redhat.com>
    LKML-Reference: <4AFB9029.9000208@jp.fujitsu.com>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    Signed-off-by: Jiri Slaby <jslaby@suse.cz>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    kernel/sched.c | 22 +++++++++++++---------
    1 file changed, 13 insertions(+), 9 deletions(-)

    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -5216,41 +5216,45 @@ cputime_t task_stime(struct task_struct
    return p->stime;
    }
    #else
    +
    +#ifndef nsecs_to_cputime
    +# define nsecs_to_cputime(__nsecs) \
    + msecs_to_cputime(div_u64((__nsecs), NSEC_PER_MSEC))
    +#endif
    +
    cputime_t task_utime(struct task_struct *p)
    {
    - clock_t utime = cputime_to_clock_t(p->utime),
    - total = utime + cputime_to_clock_t(p->stime);
    + cputime_t utime = p->utime, total = utime + p->stime;
    u64 temp;

    /*
    * Use CFS's precise accounting:
    */
    - temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime);
    + temp = (u64)nsecs_to_cputime(p->se.sum_exec_runtime);

    if (total) {
    temp *= utime;
    do_div(temp, total);
    }
    - utime = (clock_t)temp;
    + utime = (cputime_t)temp;

    - p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime));
    + p->prev_utime = max(p->prev_utime, utime);
    return p->prev_utime;
    }

    cputime_t task_stime(struct task_struct *p)
    {
    - clock_t stime;
    + cputime_t stime;

    /*
    * Use CFS's precise accounting. (we subtract utime from
    * the total, to make sure the total observed by userspace
    * grows monotonically - apps rely on that):
    */
    - stime = nsec_to_clock_t(p->se.sum_exec_runtime) -
    - cputime_to_clock_t(task_utime(p));
    + stime = nsecs_to_cputime(p->se.sum_exec_runtime) - task_utime(p);

    if (stime >= 0)
    - p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
    + p->prev_stime = max(p->prev_stime, stime);

    return p->prev_stime;
    }



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